During well drilling operations for discovery of petroleum producing zones, it is necessary to provide well drilling equipment with blowout prevention capability in the event a high pressure zone is encountered during drilling. When drilling a deep well, drilling fluid, typically known as "drilling mud" is provided with appropriate constituents to enhance the drilling of the earth formation by means of a drill bit located at the lower end of a drill string composed of a number of drilling pipe sections, drilling subs, etc. To insure that high pressure natural gas which may suddenly enter the well bore when a gas bearing production zone is encountered, the drilling fluid typically contains a quantity of weighting material that develops a bottom hole pressure exceeding the pressure of the gas that is encountered. Even though drilling fluid having a proper quantity of weighting material will prevent the occurrence of a well blowout, the hazard of well blowout is always present and thus blowout protection must be provided
Blowout preventers are typically provided with internal sealing elements which are actuated hydraulically or pneumatically by pressure responsive actuator means and which drive sealing elements, typically referred to as "packings" into sealing engagement with the drill pipe or kelly which compose the drill string. Typically, these blowout preventer packings comprise large bodies of rubber or rubber-like material which have the capability, under high pressure conditions, to deform about the drill pipe or kelly and establish a pressure containing seal therewith. These devices typically function automatically in response to predetermined annulus pressure to establish a positive seal with the drill pipe or kelly.
Drilling of the well is accomplished by rotation of a drill string having a drill bit provided at the lower end thereof. The drill string is driven by a kelly, i.e., an elongate, typically six-sided drill stem that extends through a drive aperture of corresponding six-sided configuration in a rotary table. At certain times during the drilling operation, the rotating kelly is present in the drilling well head. If high pressure conditions are encountered at this time, it is necessary to provide a seal about the kelly to contain wellbore pressure and thus prevent the well from blowing out. Obviously, any rotation of the kelly relative to the packing of the blowout preventer would damage the blowout preventer or packing and render blowout protection impossible. It is desirable, therefore, to provide a rotatable packing within the blowout preventer which has the capability of being rotatably driven by the kelly while establishing and maintaining a blowout preventing seal therewith.
Prior blowout preventers such as that disclosed in U.S. Pat. No. 3,492,007 employ horizontal forces to radially compress a packing element about a rotating drill pipe or kelly U.S Pat. No. 3,587,734 of Shaffer discloses a rotatably mounted stripper seal for a conventional stationary blowout preventer. Pat. No. 4,448,255 of Shaffer, et al. discloses a rotary blowout preventer construction incorporating an inverted truncated cone for packing deformation which establishes rotary relation with a linearly movable, hydraulically energized cone actuating piston. U.S Pat. No. 3,561,723 of Cugini discloses a stripping and blowout preventer device which also incorporates a hydraulically energized piston for achieving sealing deformation of a blowout preventer packing to prevent fluid escaping form a well in the presence or absence of a well tool such as a pipe string, while rotating or stationary, or during removal of the drill string form the well bore.
For the most part, prior art blowout preventers, including rotary blowout preventers incorporate large multi-packing elements for achieving sealing with the drill string upon being appropriately deformed thereabout. Because these blowout preventers must be tested frequently to insure operability thereof, these large rubber packings or seals frequently become sufficiently worn as to require replacement. Packing wear can also be caused during shipping operations. In the typical blowout preventer device, packing replacement typically requires well drilling down time in the order of form eight to twelve hours. This is a significant detriment to the productivity of the drilling operation as well as requiring considerable expense. It is desirable, therefore, to provide a blowout preventer packing assembly having the capability of being quickly and efficiently restored to its optimum sealing capability in only a few minutes time.
Blowout preventers typically incorporate internal chevron packings to provide a positive seal separating an oil bath chamber form drilling fluid present therein. Oil in the oil bath chamber is typically circulated continuously through the internal bearings of the blowout preventer to insure its extended service life. In the event leakage develops in an internal oil seal packing, this leakage, though detrimental to the operational capability of the blowout preventer, must be tolerated until the blowout preventer can be repaired or replaced. It is desirable, therefore, to provide a rotary or non-rotary blowout preventer having an internal blowout preventer packing assembly having the capability of being restored to its positive sealing capability in the event leakage thereof is detected without necessitating disassembly of the housing thereof. It is also desirable to provide a rotary blowout preventer having internal bearings which are continuously flushed and lubricated by flow of lubricating oil therethrough.